RU2688950C1 - Method of pressure control in closed volume and device for its implementation - Google Patents

Abstract

FIELD: physics.SUBSTANCE: invention relates to experimental aerodynamics, particularly to wind tunnels. Disclosed is method and device for its implementation, during determination of difference between preset and measured pressure can calculate fictitious or actual cross-section area of leakage/leakage slot Fand determine control element - throttling or filling.EFFECT: technical result consists in the possibility to obtain this information under conditions of incomplete information on the reason of pressure change in the wind tunnel circuit, and also to take into account the perturbing factor at pressure control, and application in automatic control system of various types of wind tunnels with high accuracy in automatic mode.2 cl, 3 dwg

Description

The group of inventions relates to the field of aerodynamics, in particular to automatic pressure control systems in closed contours of wind tunnels.

The main condition for conducting experiments in wind tunnels (ADT) of continuous action of a closed type is to ensure a given pressure in the loop of ADT. Practice shows that experiments are often accompanied by either increasing or decreasing air pressure (generally gas) in the ADT circuit for a number of reasons, including due to gaps in the design of ADT or loosely closed filling systems and / or discharge.

In the conditions of incomplete information about the causes of pressure changes in the circuit of ADT (uncertainty), it is not possible to take this factor into account when regulating the air pressure.

There is a method of setting the pressure in a controlled volume and the installation for its implementation, consisting in the fact that they set "roughly" the set value of pressure in the controlled volume of the pipeline. The pressure is periodically measured in it and, when its magnitude deviates from the set value, the amount of compressed gas that must be introduced in the controlled volume or removed from it is calculated, the value of the pressure in the controlled volume is set "roughly". The pressure is periodically measured in it and, when its value deviates from the set value, the amount of compressed gas is calculated, which must be introduced into the controlled volume or removed from it. The required amount of gas is supplied or removed, which is then “precisely” maintained in order to provide it in a controlled volume. "Precision" regulation of the pressure in the controlled volume is performed by varying the resistance of the pipeline in the control circuit when setting overpressure from the minimum value and to the maximum value, stopping the flow of gas, followed by maintaining the specified pressure in the controlled volume by briefly opening the gas inlet valve or exhaust valve to divert gas from the working capacity. When setting the pressure rarefaction - from the minimum resistance and to the maximum resistance value by turning off all the valves of the flow control elements and then the exhaust valve, stopping the discharge of gas from the working tank. Further maintaining the specified vacuum in a controlled volume with the required discreteness is performed by briefly opening the inlet valve for supplying gas or the exhaust valve for venting gas from the working tank. Installation to set the pressure in a controlled volume contains sources of high and low pressure and the input group, respectively, of the intake and exhaust valves with a control circuit. The control scheme includes an input group of valves, a gas pipeline for gas flow, and flow control elements connected in series, as well as a working tank. The inlet group of valves consists of parallel-connected inlet and outlet valves, connected at one point to the first of the n flow control elements. Sources of pressure are connected to the inlet valves through filters protecting the control system from possible contamination (Patent No. 2495392, IPC G01L 27/00 of December 27, 2011).

This method and device can be used for containers of relatively small volumes with low inertia of air distribution. For large tanks, in particular for ADT continuous action with a high inertia of pressure change, this method introduces a systematic error in the value of the measured pressure. In addition, the pulsed intake or discharge of air from the circuit of the ADT introduces perturbations in the flow, which negatively affect its quality.

The prototype adopted a device that implements the method of regulating the air pressure in the prechamber, containing a driver, actuator, temperature, pressure, position sensors, as well as a pressure regulator made in the form of a digital system of a series-connected low-pass filter and a reversed model of the control object, closed through the model model of the control object positive feedback, the controller inputs are connected to the driver and pressure sensors and air temperature in form Amer, temperature and air pressure in the gas holder, the regulating throttle position of the plunger and the nozzle throat (patent №2587526, IPC G01M 9/00 from 25.05.2016).

However, this pressure control method and the regulator are intended for batch-type ADT, having air flow into the atmosphere through a priori known area of the nozzle throat F _cr .

It is not applicable in continuous-type ADTs, since It is possible both to increase the pressure in a closed volume due to a change in the angle of attack of the model, the air inflow from the outside through the shell of the ADT circuit, and the pressure drop for the same reasons, that is to regulate pressure is necessary in conditions of uncertainty of the reasons for its change.

The task and technical result of the invention is to provide a method and creating implements its air pressure control device in a closed volume, which allows in conditions of uncertainty of the information about the cause of the pressure change in the loop count value dummy sectional area unauthorized filling the gap or air pressure relief F _w and define the regulator - throttle discharge or filling.

Solution of the task and technical result is achieved in that in the method of adjusting the air pressure in the closed volume consists in that the determined difference between the setpoint and the measured pressure in the controlled volume is calculated by this difference of the sectional area of the dummy slit leakage / leakage F _u in controlled volume and open the throttle filling or air discharge pipe line.

The solution of the problem and the technical result are achieved by the fact that the device for regulating pressure in a closed volume contains a filling pipeline with a filling throttle and its position sensor, a relief pipe with a reset throttle and its position sensor, a block for calculating the leakage / leakage section area F _y switching unit.

FIG. 1 is a block diagram of a device for controlling air pressure in a continuous-action ADT circuit, of a closed type with discharge and filling throttles;

FIG. 2 is a graph of the transient process of filling the loop with air to a specified pressure, taking into account air leakage through a fictitious slit with a cross section of _Fch4 = 0.001 m ² ;

FIG. 3 - the graph of transition of process air discharge circuit ADT into the atmosphere to a predetermined pressure with the air leaks through the dummy slit section _sch2 F = 0.001 m ^2.

FIG. 1 shows a block diagram of the inclusion of a block for calculating a fictitious area of a slot, a switching unit and a key in an air pressure control system in a continuous-action ADT circuit, of a closed type with discharge and filling throttles connected to an ADT via pipelines. Air pressure regulation is performed by filling throttles 2 and resetting 4. Gas-holders 1 are connected to an ADT 3 circuit through a regulating filling throttle 2, in the working part of which the test model is located. The control choke reset 4 connects the circuit ADT with the atmosphere. The unit required for the experiment pressure 5 is connected to the inputs of digital pressure regulators 6 and 7 and the input of the block 15 to calculate the fictitious area of the leak gap / leakage. Also, the inputs of the regulators 6, 7 and the block 15 for the calculation of the fictitious leakage / leakage gap are connected to the output of the pressure sensor 12 in gas holders, the output of the pressure sensor 13 in the pipe circuit and the sensor 14 of atmospheric pressure. The input of the regulator 6 is connected to the output of the plunger position sensor 10 (8 - plunger) of the regulating filling throttle 2, and the regulator 7 input is connected to the output of the plunger position sensor 11 (9 - plunger) of the regulating throttle 4. Leakage / leakage focal area calculator input connected to the sensor outputs 10, 11. The output of the dummy leakage / leakage gap calculation unit 15 is connected to the input of the switching unit 16, which determines whether there is a leakage gap or leakage in the ADT circuit or its absence. The output of the switch 16 is connected to the key 17, which has three positions:

- position 1 - regulator 6 and filling throttle 2 are in operation;

- position 0 - filling throttles 2 and discharge 4 are closed;

- position 2 - the regulator 7 and the reset choke 4 are in operation.

After filling the ADT with air to a predetermined pressure, formed by the setting device 5, the control throttles of the discharge 4 and filling 2 take the closed position. The input of the block 15 for calculating the fictitious gap area receives signals from sensors 10 (stroke of the filling throttle plunger 2, S), 11 (stroke of the relief throttle plunger 4, S), 12 (air pressure sensor in gas holders, Р _г ), 13 ( air pressure sensor in the circuit ADT, P ₀ ), 14 (atmospheric air pressure sensor) and calculated fictitious gap area, leakage / leakage. Further, the output signal _u F calculation unit is input to the switching unit 15, which analyzes the cross section area of the gap determines the leakage (F _u> 0.0001), leakage (F _ut <0.0001) or its absence (F _u = 0 , 0001) and generates an input signal for the key 17. The key 17 performs switching to one of three positions:

- position 1 - regulation of leakage;

- position 0 - there are no leaks and leaks;

- position 2 regulation of leakage.

If the key 17 is in position 1, the output signal from the switching unit 15 is fed to the input of the throttle controller 6, which also receives signals from pressure sensors 12, 13 and from the plunger stroke sensor of the regulating throttle filling 10. The output signal of the regulator 6 is fed to the throttle actuator input filling 2 and determines its position.

If the key 17 is in position 2, the output signal from the switching unit 15 is fed to the input of the reset throttle regulator 7, which also receives signals from pressure sensors 13, 14 and from the plunger stroke sensor of the control throttle reset 11. The output signal of the regulator 7 is fed to the input of the throttle actuator reset 4 and determines its position.

If key 17 is at position 0, then there is no leakage and air leakage, or balance each other and air pressure regulation in the ADT circuit is not required, the discharge throttles 4 and filling 2 are in the closed state

The main element of the regulators of the new regulatory system is the block for calculating the effective gap area, real or fictitious. The formulas for calculating the block are obtained from the equation of the mathematical model of the ADT, which describes the law of conservation of energy.

On the example of the equation of a mathematical model, taking into account the leakage of air from the circuit from the mass conservation equation (1):

- расход воздуха через фиктивную или реальную щель утечки;Where

- air flow through a fictitious or real leakage gap;

расход воздуха через дроссель наполнения;

air flow through the filling throttle;

ΔP ₀ = P _0zad. -P ₀ - the difference between the set and measured pressures;

K is the adiabatic index for air, equal to 1.4;

R is the universal gas constant;

T _f - air temperature in the circuit ADT, K;

T _g - air temperature in gas holders ADT, K;

V _f - the volume of the pre-chamber ADT, m ³ ;

q (λ _щ4 ) is the reduced specific air flow rate through the air leakage gap from the ADT circuit;

q ( _λrs2 ) is the reduced specific air flow rate through the filling throttle.

Air leakage to the ADT circuit is calculated according to the equation:

- расход воздуха через фиктивную или реальную щель утечки;Where

- air flow through a fictitious or real leakage gap;

- расход воздуха через дроссель сброса.

- air flow through the discharge throttle.

q (λ _щ2 ) is the reduced specific air flow rate through the air leakage slit into the ADT circuit;

q ( _λrs4 ) is the reduced specific air flow rate through the discharge throttle.

Using the equations given above, expressions are obtained for calculating the time constant T ₀ and the gain of the control object K ₀ :

- постоянная времени и коэффициент усиления для дросселя наполнения;

- time constant and gain for the throttle filling;

- постоянная времени и коэффициент усиления для дросселя сброса.

- time constant and gain for the reset choke.

As a result, we obtain the aperiodic formula for the control object:

and the drive is described by the serial connection of the integrating and inertial links:

The transfer function of the digital regulator to maintain air pressure in the ADT circuit implements the function (according to the prototype):

The factors of the regulator are calculated through the current parameters of the object of regulation:

Where:

T _ƒ is the time constant of the lowpass filter;

T _CR , K _CR - the time constant and the gain of the drive device, respectively;

The control signal of the pressure maintenance regulator in the ADT circuit implements the function:

where Δt is the time interval between the cycles of conversion;

- номера тактов рассогласования;

- mismatch clock numbers;

- рассогласование между заданным Р_0з и измеренным Р₀ значениями давления в контуре трубы на

тактах соответственно.

- the mismatch between the given P _0z and the measured P ₀ pressure values in the pipe contour on

cycles, respectively.

FIG. 2 and 3 illustrate the transient process of the air pressure in the ADT circuit to a predetermined value when the fictitious area of the leakage gap and leakage, respectively, _Fch4 = _Fch2 = 0.001 m ² .

The results of using the device are confirmed by mathematical modeling on a continuous-type ADT simulator, of a closed type with the presence of unauthorized air leaks / leaks. The process of maintaining air pressure in the ADT circuit with leakage is illustrated in FIG. 3, taking into account leakages, is illustrated in FIG. 4. As can be seen from the graphs P ₀ (t), the air pressure is maintained with a given accuracy by opening the regulating throttle by a calculated value, which compensates for air leakage / leakage. The device effectively ADT continuous closed type, and is also applicable to batch ADT when F _u = 0 m ^2.

Claims (2)

1. The method of regulating the pressure in a closed volume, which consists in determining the difference between the desired and measured pressure in a controlled volume, on the basis of which calculate the cross-sectional area of the fictitious leak / leakage gap F _y in the controlled volume and open the choke of filling or air discharge of the pipeline . 2. A device for regulating pressure in a closed volume, containing a filling pipeline with a filling throttle and its position sensor, characterized in that it further comprises a discharge pipeline with a discharge throttle and its position sensor, a leakage / leakage section calculation block F _y , a block switch.

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